Glow discharge systems



April 22, 1958 cs. BLET GLOW DISCHARGE SYSTEMS 2 Sheets-Sheet 1 FiledApril 21, 1955 INVENTOR T m E 9 n+5 saw E LL m A 0 E GM W Y B April 22,1958 G. BLET 2,832,009

GLOW DISCHARGE SYSTEMS Filed April 21, 1955 2 Sheets-Sheet 2 E; Lg EHfvv. .32 I I INVENTOR csonsss BLET Y WLM, fiwt'w m v Abbas.

operation thereof,

\ Various systems United rates Patent GLUW DISCHARGE srsTEMs GeorgesBlot, Marseille, France,

assignor to Societe I Triflnx, Marseille, France,

a society of France Application April 21, E55, Serial No. 502,802 Claimspriority, application France January 11, 1955 5 Claims. (Cl. 315-483)increase in the illumination thereof from zero to a maximum.

his a general object of the invention to provide an improved method of,and apparatus for, controlling the discharge intensity in a glowdischarge system.

Another object is to provide methods and means for gradually increasingthe illumination in a glow discharge tube in a more eflicient andeconomical way than was possible heretofore.

Another object is to tractive glow discharge and related purposes.

A further object is to provide such systems which are operated in a newand improved manner for producing a successive and gradual illuminationof all the tubes comprising the system.

Further objects include the provision of such systems, which operatemore efficiently, reliably and cheaply than heretofore and which utilizeradio frequency generating means; the provision of such systems utilizeradio-frequency generating means for supplying the tube or tubes duringthe gradually increasing illumination stage of the and a steadyalternating voltage source, network, during the steadyilluminaoperation, and the provision of such not be a source of seriousradio disprovide improved, novel and atsystems for advertising, displaytion stage of said systems which will turbance.

A further object is the provision of improved control systems for glowdischarge devices; the provision of such manner than heretofore. jTheabove and other objects and advantages of the invention, will appear thedescription proceeds.

have been proposed for so controlling a glow discharge tube as toproduce a gradual increase in the brightness of the discharge from zeroto a maximum intensity. Such a result can, broadly, be obtained byapplying to one electrode of a glow tube a variableamplitudehigh-frequency voltage, while the other electrode of the tube is held ator near zero potential, so that the discharge will gradually progressfrom the end of the tube containing the first electrode towards theopposite end. In practice, however, none of the systems reviously putforward for carrying out this idea have met with any commercial success.This failure has been due iifiiiihiiilii Patented Apr. 22, 195% tovarious reasons inherent to the design and of such prior controlsystems.

In the previously suggested systems there was provided between the highfrequency oscillation generator and the tube electrodes, an energytransmission line inductively coupled at one end with the output of theoscillation generator and at its other end with an input circuitconnected across the terminals of the tube. Since the impedance of theline must be held to a low value, and the input voltage at the input endof the line should be low whereas the output voltage at the output endhigh, the electrical efficiency of the system was necessarily poor.Moreover, owing to the presence of two inductive couplings in cascaderelation, it is practically very diflicult to obtain a correct loadingof the generator.

According to one feature of the present invention, an energytransmission line is coupled with the high frequency generator at itsinput and is connected at its output across the tube terminals, andcontains a highimpedance inductance element interposed therein in serieswith the tube input, and a capacitance in parallel across the tubeinput. It has been found that such an arrangement makes it possible toproduce a perfectly gradual illumination over a tube several yards long.

it has been recognized also that it is particularly advantageous to useradio-frequency oscillations of the order of kc. The use of suchfrequencies is desirable in the first place because it is remote fromthe broadcasting frequency ranges. Moreover, as will more fully bedescribed hereinafter, high capacity values may then be used for thecondenser connected across the tube input, in order to obtain resonancefor the input circuit while maintaining a high L/C ratio. The value ofsaid capacity may then be selected so large as to dwarf any straycapacitance present in the tube and the associated circuit. This makesit possible to construct glow system control apparatus which willoperate satisfactorily under all conditions.

According to the invention, the value of the inductive impedance in theinput circuit may be made substantially equal to the capacitativeimpedance for the resonant condition in which the input frequency equalsthe natural frequency f of the input circuit, in which condition thetube is fully illuminated.

Further according to the invention, means are provided for graduallyilluminating all the tubes in a plurality of tubes in succession,through the use of a switching arrangement, more fully describedhereinafter, whereby on ignition of each particular tube, the tube issupplied from a steady A.-C. source, and the next tube in the pluralityis then ignited. The steady source may be provided by the usualalternating means. The switching arrangement may be operated by acumming system.

Further features of the invention will appear as the disclosure proceedswith reference to the accompanying drawings wherein:

operation Fig. 1 is a simplified diagram illustrating an improvedglowdischarge system according to an embodiment of the invention; r

Fig. 2 illustrates a modified circuit;

Fig. 3 shows a further modification;

Fig. 4 illustrates a form of embodiment of the high frequency generator,connected in a circuit similar to Fig. 1;

Fig. 5 is a schematicillustration of the variable condenser arrangementand cam-operatedswitch means asso ciated therewith for automaticallyvarying the frequency of input oscillations to successive tubesaccording to a predetermined sequence;

Fig. 6 is a partial diagram illustrating the control of a plurality oftubes to be operated in succession according to the invention;

Fig. 7 shows a modified system;

Fig. 8 illustrates a circuit whereby a common high frequency generatormay be utilized both to ignite a tube gradually and to maintain theenergization thereof at a steady value.

First referring to the circuit diagram of l, a high frequency oscillator1 has its output connected with an inductance coil 2. Inductivelycoupled with coil 2. is a coil 3 connected in the circuit d serving totransmit the energy from a l1igh-frequency oscillator l. to a dischargetube 5. Connected in this circuit in series with the secondary winding 3is an inductive impedance 6 and a capacitance 7 is connected in parallelacross the tube 5. As shown, one end of winding 3 and one end of thetube 5 are grounded to provide a return connection for the circuit.

It will be noted that the circuit just described involves only a singlecoupling, the inductive coupling between windings 2 and 3. Moreover, thearrangement of inductance coil 6 and capacity 7 malt-es it possible toimpart to the circuit the requisite characteristics for obtaining ahighly smooth and gradual illumination of the tube as the R.F.energizing voltage applied to the tube is increased.

With the glow tube 5 cut off, the R.-F. frequency input voltage isapplied to the upper terminal 5a thereof and the amplitude of the inputvoltage is gradually increased in a manner to be later described. As theinput voltage is increased, the tube lights up gradually along itslength until it has become entirely illuminated throughout. t

Instead of the circuit shown in 1, alternative circuits may be used asillustrated by way of example in Fig. 2 and in Fig. 3. In the Fig. 2modification, the coupling of the input energy is produced by means ofan auto-transformer 8; while in the modification of Fig. 3,- acapacitative coupling is used, by means of the condensers 9. In otherrespects both the circuits of Figs. 2 and 3 are similar to theembodiment disclosed in connection' with Fig. 1.

Any suitable type of oscillator may be utilized in accordance with theinvention, for deriving the variableamplitude input voltage for thetube. Fig. 4 illustrates one particularly desirable type of oscillatorcircuit usable for the purposes of the invention. The circuit includesan oscillator stage 10 comprising a conventional triode having aresonant circuit consisting of an inductance 12 and condenser 11a inparallel connected between the grid and anode thereof. A mid-point ofthe inductance 12 is connected to the cathode and to ground. Connectedbetween the anode and ground i a variable condenser 11 serving to adjustthe output frequency of the oscillator. The output winding 12 isinductively coupled with a winding 13 insertedin series with the controlgrid of an output amplifier tube M, and the anode of this tube hasconnected with it a parallel resonant circuit including a condenser inparallel with an inductance winding 2, which serves as the primarywinding likewise designated 2 in any one of Figs. 1, 2 and 3. Theremainder of the circuit of Fig. 4 has been shown identical with thecircuit of Fig. 1, but it will of course be understood that this part ofthe circuit may instead be made identical with Fig. 2 or with Fig. 3.

In operation, adjustment of condenser 11 varies the frequency of theoutput produced by oscillator 1t} and hence varies the output frequencyfrom power tube 14. As a result there is applied across the input ofglow tube 5 a variable voltage which has a minimum amplitude when theover-all circuit is far from its resonant condition and which graduallyincreases in amplitude as the' circuit approaches resonance.

Let f the resonant frequency of the circuit'comprising inductance 3,line 4, inductance 6, condenser 7 and glow tube 5; this is the frequencyvalue for which the glow tube 5 is fully illuminated. The resonantfrequency t may be approached in either of two ways, i. e. starting fromlower frequencies or starting from higher frequencies. In practice it isdesirable to start from the higher frequencies and to reduce thefrequency until resonance has been reached. This procedure is preferablesince on ignition of the tube its capacity rises due to the ionizationof the gas therein; hence the quantity diminishes; therefore if onestarts from frequencies above the resonant frequency and as thefrequency is gradually reduced, the quantity just noted will be variedin the same sense as the frequency, so that a very gradual increase inillumination of the glow tube is obtained.

As previously stated herein, the oscillator may be used for graduallyilluminating in succession a number of glow tubes constituting, forexample, an advertising sign or the like. Fig. 5 illustrates a circuitarrangement suitable for such purpose. As shown, the variable condenser11 of Fig. 4 is herein replaced by two condensers in parallel eachdiagrammatically indicated as comprising a fixed electrode 19, 20respectively, and a rotatable elec trode 15, 16 respectively. Themovable electrodes 15 and 16 of the two condensers are displaced fromeach other and are secured on a common shaft 17 adapted to be driven inrotation from a suitable electric motor 18. The fixed electrodes 19 and2d are connected to the respective fixed contacts of a reverser switchwhose movable reversing contact arm 22 is connected to the anode of theoscillator tube Hi. The reverser switch arm 21 is actuated between itspositions in engagement with the two fixed contacts, by a cam device 22driven from motor 18 through a suitable transmission indicated in dottedlines.

In operation, it will be apparent that the two variable condensers aremade alternately operative and the adjustments may readily be made insuch manner that, as soon as one glow tube has become fully illuminated,this condition being reached when one of the condensers has attained itsmaximum capacity, the frequency is suddenly switched back to a value forwhich the said tube is cut off, owing to the fact that the firstmentioned condenser is switched out of circuit by the action of thereverser switch and the other condenser, which at the time stands at itsminimum capacitance value, is connected in circuit instead. Now the nettube is gradually made to glow until it is fully illuminated, whereuponit is cut off and the cycle is repeated. It will be apparent that thisarrangement can be used with any number of glow tubes which can thus bemade to light up gradually in succession, each tube being cut off as thenext tube of the series starts to glow.

In order to maintain the discharge in the tube after it has beenignited, switching means may be used whereby a tube on being fullyignited is thereafter supplied from a steady frequency source, at radiofrequency or network frequency. Such a switching arrangement may beuperated in synchronism with the switching arrangement described in theforegoing paragraphs, in such a way that on ignition of any tube thevariable R.-F. input is disconnected therefrom and theconstant-frequency source is connected thereto instead. An example ofone such arrangement is illustrated in Fig. 6.

A plurality of glow tubes, e. g. three as shown, are indicated at 5, 5and 5", and may for example form parts of'a shop sign, e. g. they may beso shaped and disposed as to form the letters of a name, etc. Each tubehas one terminal grounded and the other terminal connected across theline 4 through a respective switch 23, 23, 23". With the tubes cut off,a R.-F. voltage is gradually applied to the terminal 5a of the firsttube 5, and its amplitude is gradually increased in the manoneness nerindicated above. As the applied voltage increases, the tubeprogressively becomes illuminated along its length until it glowsthroughout. At this time the switch 23 disconnects the tube 5 from thevariable-amplitude energizing R.-F. source and connects the sourceinstead to the line 4' for energization of the next tube 5.

Moreover, there is associated with each switch 23, 23', 23", a switch24, 24, 24", so connected that whenever a switch 23 disconnects therelated tube from the variable voltage source, the switch 24 associatedtherewith will connect the tube to a constantfrequency supply sourcewhich will serve to maintain the discharge therein.

In the exempiary circuit illustrated in Fig. 6, the constant amplitudesupply is provided by the normal A.-C. network, through suitabletransformers 25, 25, 25". Choke coils 26, 26', 26 are provided forblocking the high frequency during the starting period.

The ganged switches23-24, 23'24, 25"25", are operated by cams drivenfrom a motor 18, the shape and setting of the cams being sopredetermined as to cause them to perform the desired functions with therequisite timing, that is, successively to disconnect each tube as ithas been ignited from the variable-amplitude high frequency source, andconnect it instead to the fixedamplitude low frequency source formaintaining the tube in ignited condition and simultaneously connectingthe next tube to the variable-amplitude high-frequency source.

Fig. 7 illustrates a modified circuit wherein the discharge in theignited tubes is maintained by energization from a steady-voltage highfrequency source. In other respects this circuit operates in the samemanner as described in connection with Fig. 6.

After all the tubes such as 5, 5, 5", etc., forming the electric shopsign or the like, have been ignited, they may be simultaneouslyextinguished and then the cycle may be recommenced by graduallyre-igniting the initial tube, and so on. The shaping and setting of thecams can readily be determined to produce the desired cutoff of all thetubes at the end of a cycle.

It should however be noted that the shaping of the cam contours must bedetermined with great precision in order to avoid having some of thetubes remain in ignited condition even a short time after the remainingtubes have been cut off. Moreover, even where the cams are accuratelyformed and set originally, wear is apt to affect this condition aftersome time. Accordingly, a different arrangement may be provided inaccordance with the invention to produce the desired simultaneouscut-off of all the tubes at the end of each cycle.

The arrangement comprises a switch 27 operated by a cam so as to cut offthe supply circuit to the screen grid 29 of the output triode 14 as soonas the last glow tube of the series has become fully illuminated, andanother cut-0E switch 28 ganged with cut-off switch 27, forsimultaneously cutting off the supply circuit.

As shown in Fig. 8, an oscillator 30 may be used which yields aconstant-amplitude high frequency output (e. g. at 120 kilocycles),which output serves to supply two circuits of the system. One circuitcomprises a variable impedance 31 and the control grid of output stagetetrode 14, whereby said grid may be operated at a variable voltage andthereby a high constant frequency, variable amplitude input may beobtained for igniting the glow tubes. The other channel includes anamplifier 32 whose output provides the fixed amplitude high frequencyinput required to maintain the discharge in the tubes.

It will be understood that the invention is not to be limited to theforms of embodiment illustrated and described, but that variousmodifications may be made therein, particularly as to the type ofoscillator used to derive the variable-amplitude, high-frequency voltagesupplying the glow tube or tubes. Similarly, apparatus according to theinvention may be applied in such a way as to produce a gradualillumination of a tube starting from both ends together and progressingtowards the middle of the tube for which purpose an artificial zeropoint may be established intermediate the ends of the tube. The glowtubes used may be of the known type wherein internal electrodes areomitted, and replaced by externally located armatures.

What is claimed is:

1. In a luminous display apparatus for progressively illuminating agaseous discharge tube, input terminals for said tube, a high frequencygenerator, primary windings, secondary windings, a circuit connectingsaid high frequency generator and said primary windings, a variablecondenser connected in said circuit for varying the frequency suppliedto said primary windings from an initial to a final value, a secondcircuit connecting said secondary windings to said terminals, aninductance in said second circuit and a condenser connected across saidterminals, said second circuit including said second named condenserhaving a resonant frequency approximating the final value of thevariable frequency whereby when the variable frequency is progressivelyvaried said tube will be progressively illuminated to completeillumination at the resonant frequency of said second circuit.

2. Apparatus as claimed in claim 1 in which said high frequencygeneratorincludes a triode and said variable condenser is connectedbetween the anode of said triode and the ground.

3. In a luminous display apparatus for progressively illuminating agaseous discharge tube, input terminals for said tube, a high frequencygenerator, primary windings, secondary windings, a circuit connectingsaid high frequency generator and said primary windings, a variablecondenser connected in said circuit for varying the frequency suppliedto said primary windings from a high frequency progressively to a lowerfrequency, a second circuit connecting said secondary windings to saidterminals, an inductance in said second circuit and a condenserconnected across said terminals, said second circuit including saidsecond named condenser having a resonant frequency approximating thelower frequency of the variable frequency whereby when the variablefrequency is progressively reduced said tube will be progressivelyilluminated to complete illumination at the resonant frequency of saidsecond circuit.

4. In a luminous display apparatus for progressively illuminating agaseous discharge tube, input terminals for said tube, a high frequencygenerator, primary windings, secondary windings, a circuit connectingsaid highfrequency generator and said primary windings, a variablecondenser connected in said circuit for varying the frequency suppliedto said primary windings from a high frequency progressively to a lowerfrequency, means connecting one side of said secondary windings to aterminal of said tube, an inductance connected in series in said means,means connecting the other side of said secondary windings and the otherterminal of said tube, and a condenser connected across said terminals,said connectmeans, said inductance and said condenser comprising asecond circuit having a resonant frequency approximating the lowerfrequency of the variable frequency whereby when the variable frequencyis progressively reduced said tube will be progressively illuminated tocomplete illumination at the resonant frequency of said second circuit.

5. in a luminous display apparatus for progressively illuminating agaseous discharge tube, input terminals for said tube, a high frequencygenerator, an output winding connected to said generator, variablecondenser means for varying the frequency supplied to said outputwinding from a high frequency progressively to a lower frequency, anoutput amplifier tube having a control grid, a winding connected inseries with said control grid and inductively coupled to said outputwinding, primary windings connected to said amplifier tube, secondarywindings, a circuit connecting said secondary windings to saidterminals, an inductance in said circuit and a condenser connectedacross said terminals, said circuit inclnding said condenser having aresonant frequency approximating the lower frequency of [115 variablefrequency whereby, when the variable frequency is progressively reducedsaid tube will be progressively illuminated to complete illumination atthe resonant frequency of said circuit.

References Cited in the file of this patent UNITED STATES PATENTS Seamanet al. June 28, 1938 Seaman et al. Sept. 10, 1940 Atkins et al. Aug. 12,1947 Short Dec. 21, 1948 Rosseau Jan. 17, 1956

